This study explores the hypothesis that dieting-induced changes in functional activity of the central neurotransmitter serotonin are correlated with impaired satiety responses. This change in satiety responses may contribute to difficulties experienced by overweight persons with regard to weight management. This placebo-controlled study, using a fixed order design, will examine the effects of a 4 week reduced caloric diet on serotonin precursor availability and satiety responses in healthy normal weight women. Results of this study will lend to further understanding of normal biobehavioral responses to dieting. This is a core lab study only.